A. Field of the Invention
This invention relates to a foil composite material, to a method for manufacturing the foil composite material, as well as to a card body, in particular a card body for a portable data carrier, which contains the foil composite material, and to a method for manufacturing the card body.
B. Related Art
In the production of card bodies, in particular for portable data carriers, such as e.g. chip cards, several plastic foils lying one over the other are laminated to each other. As plastic foils there are usually employed thermoplastic foils because of their good laminatability, e.g. foils made of polyvinyl chloride, polycarbonate, polypropylene, polyethylene terephthalate or thermoplastic polyurethanes. A disadvantage of card bodies made of such thermoplastic foils is their deficient mechanical properties with regard to bending stress and the action of impact force. There result stresses in the card body, and finally cracks. The installation of electronic modules also usually leads to stresses, a weakening of the card body, and ultimately to an elevated susceptibility to cracks and breaks.
To improve the mechanical properties of such card bodies it is advantageous to employ foils made of thermoplastic elastomer, for example based on urethane, within the framework of the laminating process. These foils are exceptionally elastic and can considerably improve the bending strength and breaking strength of the card construction. In the print EP 0 430 282 A2 there is described a card body in the form of a multilayer identification card wherein a layer of thermoplastic elastomer is respectively provided between the card core and corresponding cover foils.
However, it is very difficult to process foils made of thermoplastic elastomer, so-called TPE foils, within the framework of a laminating process upon the manufacture of a card body. On account of their high elasticity the foils are very “limp”. The lack of stiffness leads to problems upon processing in the production machines, and the low dimensional stability can also cause register problems upon printing of the foils. In addition, the material tends to flow out upon laminating. Further, such foils possess a low glass transition range, which lies under 0° C., whereby it remains flexible and does not become brittle in this temperature range. Furthermore, the foils tend to block upon stacking on account of their smooth surfaces, so that the foils in a stack are hard to single and transport. To obtain a sufficient connection stiffness upon lamination of such foils to other materials such as polycarbonate, polyethylene terephthalate, polyethylene terephthalate copolyesters or blends of polyesters and polycarbonate, it is moreover necessary to reach the glass point of the respective other material. Because this glass point regularly lies far above the glass transition range of thermoplastic elastomers, this frequently leads to the thermoplastic elastomer floating off, in connection with the dependence on the strength of the viscosity drop in the corresponding temperature range. This has the consequence that the employed laminating machines must often be cleaned. In some cases the foils adjacent to the thermoplastic elastomer can even likewise start to flow, and deform a printed image located thereon. Although it is possible to laminate at lower temperatures to thereby prevent the foils from floating off, an insufficiently good laminate bond is normally obtained upon laminating at low temperatures.
These problems already occur when employing the foil thicknesses of 100 μm to 300 μm that are usual in the manufacture of data carriers. To appreciably protect a data carrier against the risk of breakage, however, it is usually already sufficient to incorporate into the construction on both sides, as far outwardly as possible, layers made of thermoplastic elastomer that are only approximately 30 μm to 50 μm thick. However, these thicknesses are difficult to handle in conventional processing operations. Even very stiff foils such as polycarbonate foils can no longer be processed at layer thicknesses of 50 μm or therebelow.
Hence, it is desirable to combine the positive properties of relatively stiff thermoplastic foils and of foils made of thermoplastic elastomer in a single foil material. A solution approach in this direction is disclosed in the document EP 0 384 252 B1. The therein described foil composite material has a multiplicity of layers, whereby a middle layer is made of thermoplastic elastomer. This layer is adjoined by layers made of thermoplastic plastics. Upon the manufacture of the composite there are applied to a foil forming the middle layer the further layers. One application method is simultaneous extrusion.